# Analysis of the stability of the system characterized by the transfer function

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Sebastian Alexandru on 18 Aug 2020
Answered: Paul on 26 Aug 2020
Hi all,
I also have a problem to solve in the field of "systems theory". I solved the mathematical part, but now I have to find a virtual method for analyzing the stability of the system characterized by the transfer function. Therefore, I chose matlab.
I need to graphically display the Nyquist diagram and the poles and zeros of the transfer function.
Transfer function: The code for the Nyquist diagram is as follows:
num=[1 1]
den=[1 1 4 1 2]
G=tf(num,den)
plot(nyquist(G))
grid on
The code for representing the poles and zeros of the transfer function is as follows:
num=[1 1]
den=[1 1 4 1 2]
G=tf(num,den)
plot(pzmap(G))
grid on
How could I see on the same graph both functions or one below the other?

Paul on 26 Aug 2020
Does this do what you want:
>> nyquist(G)
>> [P,Z]=pzmap(G);hold on;plot(real(P),imag(P),'x'),plot(real(Z),imag(Z),'o')

R2019a

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